By Dong Sun-hwaSinger-actor Seo In-guk will return in the tvN series "Hundred Million Stars from the Sky" in September after being embroiled in a controversy. Seo, 30, started mandatory military service on Mar. 28 last year, but was released after only four days due to symptoms of osteochondritis dissecans (OCD), a disorder that causes swelling and pain in the joints.He was exempted from mandatory military service. But, some people insisted that Seo deliberately did not receive treatment before his enlistment. "We were not aware that OCD could be a ground for exemption," said a spokesperson for Jellyfish Entertainment, Seo's former agency. "We neither neglected nor aggravated the condition on purpose.""Hundred Million Stars From The Sky" is a remake of the Japanese drama of the same name. Despite its popularity in Japan, the drama could still cause controversy because it deals with incest. Actress Jung So-min will be Seo's partner in the series. Seo debuted as a singer in 2009, after appearing in the first season of Mnet's talent show "Superstar K." He topped the competition and gained success as an actor thanks to hits including the tvN drama "Reply 1997."